Electrically heated apparatus and method of operating



p 1936- G. A. PATTERSON 2,052,649

ELECTRICALLY HEATED APPARATUS AND METHOD OF OPERATING F iled Sept. 10, 1932 5 Sheets-Sheet 1 6 y Fig. F'zyzi- 3 3' m l 1 z Q2 2% W1 INVENTOR ATTORNEY Sept. 1, 1936. G. A. PATTERSON ELECTRICALLY HEATED APPARATUS AND METHOD OF OPERATING Filed Sept. 10, 1932 5 Sheets-Sheet 3 INVENTOR eory 4. Pa 776/00/7 BY f ATTORNEY Sept. 1, 1936. G}. A. PATTERSON ELEGTRICALLY HEATED APPARATUS AND METHOD OF OPERATING Filed Sept. 10, 1932 5 Sheets-Sheet 4 n w o E M N f fm W n A Patented Se t. 1, 1936' V .zsszsis ELECTBICALLY HEATED APPARATUS AND METHOD-F OPEQATING George Anthony Pattei-son, 'B ui'ialo, N. Y., as- Signor to Nationalidniline and Chemical Compuny, New York; N;'Y., acorporation oi New York Application September 10.119312, 801111 No. 632,544

18 Claims. (cigars-4'2) My invention relates to electrical heating apparatus and methods of using the same, andv particularlmto devices for heating materials by induction. l, 5 The ordinary induction heater comprises a primary consisting of a number of turns of wireconnected to a source of alternating current with the turns encircling a member formed of conducting material which serves as a secondary.

In heaters of this type the application of alternatlng current to the primary induces current flow in the secondary which causes the memberserving as the secondary to be' heated. Ifhe primary usually consists of a large number. of turns oi! wire, whereas the secondary conslsts'oi' a member to be heated, which may be a mass or metal, a metallic vessel, or other metallic member.

The patent to Davis 1,680,595, dated august 14, 1928 describes an induction heaterapplled to a vessel for heating liquids containedtherein in which the vessel constitutes the secondary and current is induced in the vessel by the action of alternating current supplied to a primary to heat the vessel and its contents. The Davis patent also describes means for generating heat substantially uniformly throughout the walls of the vessel during operation and means for varying the current flow in the primary so that the current induced in the vessel and the heat applied to the liquid may be varied.

Induction heaters possess considerable advantage over electrical heaters in which heat is generated by resistance elements. The cost of oper- 35. ating induction heaters is much less than that of operating resistance heaters, and heat may be concentrated and high temperatures produced and maintained in induction heaters more readily than with resistance elements because 0! the 40 dii'ilculty presented in arranging a large number of resistance elements in a limited space. Moreover induction heaters may be used for developing heat in the member to be heated or in the case of a liquid the heat may be developed in a member in direct contact with'the liquid whereas resistance elements are ordinarily placed adjacent to the member to be heated and heat the same by radiation and convection. However, resistance elements possess the advantage that they may be used in applying heat in varying amounts to diiferent parts of a vessel or other member to be heated. This flexibility of operation has not heretofore been obtained by the use of induction heaters.

My invention is an improvement over induction heaters such as that described in the Davis patent in that the location as well as the amount or heat developed is selectively controlled to ob- 'tain the desired application of heat. This feature of my invention is of particular advantage 5 .in heating stills or other vessels in which liquids are heated and in which the level of the liquid varies during operation.

Among the objects of my invention are to provide a method and means for heating materials 10 by induction in which the location of the heat applied, the area of the member heated and the amount of heat generated therein are selectively varied, to provide novel constructions and arrangements of the elements of the heater, and to 15 provide a method of distilling liquids whereby overheating of the apparatus and overheating and refluxing oi the vapors may be avoided.

These and other objects and features of my invention will appear from the following descrip- 20 tion thereof.

As applied to a still or the like, my invention provides for theapplication of a large amount of heat to that portion of the vessel in contact with the liquid, whereas that portion of the vessel in contact with the vapors above the liquid may not be heated at all or may be heated to a comparatively low temperature sufllcient to prevent refluxing of the vapors in the still. Furthermore, the area of the vessel to which a large amount of heat is applied may be varied so that as the level of the liquid is progressively lowered during distillation, the area in which the greater amount of heat is generated is progressively decreased and confined to substantially that por- 35 tion oi! the vessel in contact with the liquid being distilled. In this way the upper portion of the vessel does not become overheated and danger of cracking the vessel dueto uneven expansion thereof ,is avoided. Moreover, the vapors pro- 40 duced are not. overheated or decomposed by contact with the surfaces which are at excessively high temperatures.

Although my invention is particularly adapted for use in heating stills and vessels containing 1;, liquids, it will be apparent that my invention may also be applied in heating other materials or devices, as for example autoclaves, storage tanks, kettles, and apparatus-for promoting catalytic reactions such as the apparatus disclosed in United States Patent No. 1,604,739 to C. R. Downs. However, for the purpose of illustration the invention will hereinafter be shown and described as applied to a still and to a refluxing kettle.

In the drawings:

- Fig. 1 is a side view partly in section showing a still provided with a heating device constructed in accordance with one of the preferred forms of my invention;

Fig. 2 is a view taken at right'angles to Fig. 1, showing the arrangement of details of the construction;

Fig. 3 is a sectional plan view on section line 3-3 of Fig. l of the portion of the apparatus shown in Figs. 1 and 2;

Fig. 4 is a perspective of a detail struction;

Fig. 5 is a wiring diagram showing the arrangement of the circuit elements of the form of the apparatus illustrated in Figs. 1 to 4;

Figs. 6 to 9 inclustive are diagrammatic illustrations of various adjustments of the heating elements;

Fig. 10 is a view, partly in section, partly in ele-. vation showing a kettle provided with a modified form of heating device constructed in accordance with my invention;

Fig. 11 is a plan view of the heating apparatus of Fig. 10, the vessel Hi2 and supporting lugs being removed from. the supporting legs to more clearly show the induction coil mounting;

Fig. 12 is a section on line l2ll2 of Fig. 11 showing details of the coil arrangement and coil bracing;

Fig. 13 is a detail of one of the coil insulating members;

Fig. 14 is a wiringdiagram showing the arof the conrangement of the circuit elements in the modification of the invention illustrated in Figs. 10 to 13; and 1 Figs. 15 to 18 inclusive are diagrammatic illustrations of the various adjustments of heating elements obtainable by the circuit arrangement of Fig. 14.

In the construction shown in Figs. 1 to 9 of the drawings the still comprises a vessel having vertical walls 2, and a hemispherical bottom 4. The walls 2 of the vessel are provided with an annular rim 6 adjacent the top of the vertical walls to which acover for the vessel may be secured. An annular flange 8 formed integrally with the vertical wall 2 of the vessel, extends outwardly from the walls thereof and is spaced a short distance below the rim 6. The flange 8 is provided with a plurality of openings ill spaced about the flame through which pass bolts l2 for supporting the primary of the induction heater. The lower portions of the bolts i2 pass through brass supporting bars l3 supporting vertical rods Hi which extend downwardly adjacent the walls 2 of the vessel. The rods l6 are threaded on each end and are secured by nuts to the supporting bars l3 carried by the bolts 82. Tie bars Hi and M" which also may be of brass or other suitable material are provided at the upper and lower ends of the rods it to hold the rods in spaced position adjacent the walls of the still.

A conductor 26 which constitutes the primary for the heater is shown in the form of a conductor of rectangular cross section extending in a coil .about the vertical wall of the vessel between the rods H5. The turns of the conductor are spaced vertically by means of suitable insulating plates 68, each of which is provided with holes through which the rods i6 extend. The

V conductor may comprise any suitable number of turns depending upon the amount of current which the conductor is to carry and the amount ofheat which is to be developed in the wall of the vessel. The conductors are insulated from tie bars M and M by means of insulating blocks 2! and M respectively. The rods on each side of the ends of thev conductors are provided with insulating bars 22 and 22' instead of the blocks 25 and 2d. The bars 22 and 22 extend beyond the outer rods iii and together with insulating cross- -members 23 or 23' provide supports for the conductorleads. Lock nuts on the rods to hold the tie bars and insulating blocks in position forming a unitary structure loosely supporting the conductor Zil.

The terminal for the upper end of the conductor is illustrated in Fig. 4 with the lead 26 connected to the conductor extending at right angles to the turns thereof. The lead 26 may be suitably brazed or otherwise secured to the conductor 2d and rests on the insulating bar 23 between insulating blocks 25 and 25'. The lead may be clamped in position by means of an insulating member 2? bolted or otherwise secured to bar 23. The bar 23 is secured by bolts to the blocks 22 on each side of the conductor lead 26. The leads connected to the opposite end and intermecliate points of the conductor may he similarly constructed providing a support for the con.- nection which protects the same from injury.

- The conductor which constitutes the primary for the heater, preferably is formed in a plurality of sections which in turn may be subdivided into smaller sections. In the form of the invention shown in the figures of the drawings the conductor 2G is provided with an upper section 2 1 connected through switching mechanism to a suitable source of alternating current by the lead 26. The lower portion of the section 24 is similarly connected by the lead 28 through a switch to the source of alternating current. A third lead 3d extends from a point intermediate the ends of the conductor section 26 to the source of current is rot subdivided into portions but it will be apparent that provision may be made to divide either section into as many subdivisions as desired and that more than two conductor sections may be used if preferred.

The still is preferably provided with an additional conductor 30 in the form of induction coils positioned adjacent the hemispherical portion of the bottom of the vessel in order to heat the bottom thereof uniformly asdescribed in the patent to Davis mentioned above. The construction and arrangement of the coils of conductor 40 are illustrated for convenience as similar to those of the Davis device. However, if desired, the coils 40 may be omitted altogether although ordinarily the conductor 40 is employed when it is desired to heat the contents of the still to a high temperature. The coils of conductor Q0 are connected to the source of alternating current by leads 62 and i l independently of the conductor 20.

That portion of the vessel to which the conductors 20 and 6B, which constitute the primary of the heater, are applied, is preferably enclosed within a heat insulating casing 416. A panel 08 to which the leads from conductors 22 and 42 pass, is positioned so as to provide convenient aocess to the electrical circuit.

In order to control the flow of current selectively so that the sections of the conductor 20 may be included in the circuit and the current flow through said sections varied to apply the desired amount of heat to that area of the still adjacent the various sections of the conductor 20, switches 22 and I2 are provided. An additional'switch 54 in circuit with the conductor is'also employed to connect and disconnect that portion of the primary adjacent the hemispherical bottom of the still with. a source of alternating current.

The circuit arrangement preferred for controlling the current flow through the conductors 22 and 40 of. the primary is illustrated in Fig. 5.

In this arrangement the switch is a three-pole double throw switch and switch 52 is a singlepole double throw switch. Switch 54 which controls the operation of conductor 40 maybe a single-pole single-throw switch operated independently of the operation of the switches ill and 22. The lead 22 connected to the upper end of the conductor section 24, is connected to the left hand contact 62 of the switch 22, and the switch- 7 52. The opposite contact 54 of the switch 52, on

the right side of the switch as illustrated, is connected to upper blade 66 of the three-pole switch 52. The lower end of conductor section 24 is connected by lead 28 to the lower switch blade 68,

and the lead 20 which is connected to an inter mediate point in the section 24, is connected to the upper left contact 10 of the switch 50. The upper end of the lower conductor section 22 is connected by the lead 24 to the middle switch blade I2 of the switch 50 while the lower end of the section 32 is connected through lead 22 to the lower right contact ,14 of the switch 50. 'Ihe upper right contact 18 is blank and the middle and lower left contacts 18 and 80 are connected to each other. The source of alternating current 22 isconnected to the circuit through the middle and lower right contact 20 and I4 of the switch 50.

In operating the device with the foregoing circuit arrangement in heating or distilling liquids the circuit is controlled to provide four adjustments of heat independently of the application of heat to the vessel through the operation of the conductor 40. Thus. when the vessel is filled with liquid to a point above or adjacent to the upper end of the section 24 of the conductor, the switch 52 is thrown to the right and the switch 82 is thrown to the left to develop the maximum heat in the vessel and bring the liquid to the desired temperature or to heat it to boiling. When the switches are in this position the conductor sections 24 and 22 are connected in parallel as shown atically in Fig. 6 of the drawings. Current then flows from source 82 to contact 20 thence through conductor 52, switch blade 56, and lead 22 to conductor section 24 and back through lead 22 and switch blade 22 to contact I4 and the opposite side of the current source 22. Current also flows in parallel from current source 22 through contact 20. switch blade I2 and lead 24 to conductor section 22 and back through lead 22 to contact 14 and current source 22. The current flow in this circuit arrangement is l tively large so that the heat developed ins-the vessel is large and extends through substantially the whole vertical wall thereof. Heat may also be'developedin the hemispherical portion of tbe vessel by closing switch 44' tosupply current to' conductor 42.

As distillation continues and the level of the liquid in the vessel is lowered, the switch blade 56 of switch 22 is thrown to the right engaging contact 64 and the switch 50 is thrown to the left. With' the switches in these positions, current passes from the current source through connection 88, switch blade 85, contact 24, switch blade 88, contact 10, connection 20, the lower portion of conductor 24, connection 22, switch blade 62, contacts and 12, switch blade 12, connection 24,- conductor 22, connection 22, and thence to the current source. With this path of current flow the upper portion'of conductor 24 is disconnected while the lower portion is arranged in series with conductor 22. Such an employment of' the heating element is shown diagrammatically in Fig. 7 of the drawings.

When the level of the liquid in the'vessel falls still lower, switch 50 is moved again to the right while the switch blade 56 of switch 52 remains in engagement with contact 64. only the lower conductor sections 22 and 40 re-' main in. circuit. as shown diagrammatically in Fig. 8 and only the lower portion of the vessel is heated. i i

When the liquid level in the vessel has dropped to the top of coil 40, it may be desirable to supply a low degree of heat to the upper portions of the vessel to prevent condensation of liquid on the walls. For this purpose the conductor sections are, connected in series as shown diagrammatically in Fig. 9 by throwing bothswitch 50 and switch 52 to the left. Current then passes from current source 82 through contact 60, connection ductor section 24 and through lead 28, switch blade 68, contacts 80 and i8, and switch blade 72 to lead 24 connected to the lower conductor section 22. Current then passes back through lead 28 and contact 14 to the current source. The coil 40 is connected to a suitable current source. The lower induced voltages afforded by the series connection of coils 24 and 32 reduces the current flow, and the zone of most intense heating is'restricted to the portion of the vessel occupied by liquid. Overheating of the upper portions of the vessels is consequently avoided.

The foregoing method of operation ensures the application of heat to that portion of the vessel in contact with the liquid therein while the up- In this position per portion of the walls of the vessel are not overheated so that undue expansion thereof does not take place and danger of cracking or distorting the vessel is obviated. Furthermore, the walls of the vessel, being at comparatively low temperatures, do not cause decomposition or cracking of the vapors distilled off of the liquid in the vessel and coming in contact therewith.

In any of the above circuit arrangements the conductor 40 may be connected or disconnected from the source of current as desired. When the level of the liquid in the still has fallen below the lower conductor section 22, the distillation may still be continued by means of the conductor 40. All or a portion of the walls of the vessel may be heated as distillation continues by adjusting the of the vessel to cool.

Figs. 10 to 12 of the drawings illustrate a modi- 75 fled construction of the apparatus of inven=- tion. The induction heater illustrated in these figures is especially suitable for the manufacture of dibenzylsuccinate, dichlorbenzylchlorlde, Carbanthrene blue green FFB, for use in the purification of methyl-benzanthrone, and for similar processes.

-With special reference to Fig. 10 of the drawings, vertical tubular supporting legs Edi are circumferentially disposed about an enamel-lined kettle I82. At thetop of the" tubular members icI, lugs not are provided to support the rim of the kettle. The lugs I08 are secured to the vetrical supporting members lot by means of bolts m l. Thetop ltd oi thelrettle is shown clamped to the kettle by means oi-clamps ltd mounted on the lugs Hi3. I

A tubular sleeve ml is fitted over each of the vertical supporting members tilt and may be suitably affixed thereto, as for example by means of bolts mo. Mounted on the sleeve are radially disposed stepped coil supporting members or plates I09. Each step of the supporting plates no is provided with a plate Mil adapted to support an induction coil. Suitable bracing flanges or gussets ill are provided on the plate i239 for additionally strengthening the plates lid. The horizontal flanges 9 l2 may also be providedto give additional rigidity to this member. The plates we may be amxed to sleeves itl in any suitable manner as by brazing, wel, etc. depending upon thematerials used for their construction. The supporting and bracing members may be constructed of brass or other suitable material.

Mounted on the plates Mil oi the supporting members I09 are a series of electrical conductors or coils IE3 to ill which constitute the primary of the induction heater. 'ese coils may consist of solid magnet wire suitably ted with asbestos or other suitable heat resistant insulation, and each coil is preferably covered with asfirmly in position by means of vertical rods 023 and i241. Arcuate separating plates l25 of suitable insulating material, such as ebony asbestos wood, are provide'dto maintain the coils spaced from one another. A plan view of one of the insulating members I25 is shown in Fig. 13, the

holes l28 being provided for the passage of rods E23, I24. End plates ortie bars 026 and I26 of brass are provided tosuitably space the rods I23;

124, andto hold the coils in position. These sleeves I07 may be fitted over supporting members IIlI; the kettle may then be pu position, and the sleeves adjusted along supporting memf" illI until they are in suitable position with spect to the kettle, whereat the tubular members [0! .maybedrilled and bolts 08 inserted.

actress leadlineflilil tocoil llt. Coils Him, Ms, M6, and ill are arranged in series, coil-ll'l being connected by means of line E33 to the arm 834 of a single pole two-throw switch H35. One contact X136 or this switch is in turn connected to line Illll returning to the current source 538. The other contact H38 is connected through line I39 to coil M8. Coils H8 and M9 are serially arranged, and coil Ill) is connected through line i -id to coil 512i), and through line ldl to contact M2 of switch M3. The coil 6% is connected to coil I26 and also by means of line I436 to contact M5 of the switch I53. The coil G28 at its end remote to coil no is connected through line M8 to contact Ml of switch 568.

with this circuit arrangement .four adjustments of the circuit may be obtained, inducing current into" and thus efiecting heating of yarious desired portions of the kettle m2.

Referring to Fig. 15, when the arm 53d of switch i535 is in the up position, i. e. connected with the contact let, the current will pass in an electric circuit through line i32, through coils M3, M6, M5, M6, and ill in series, through line 833 to the arm ltd, through arm i536 and contact H36 to the line lal. and thence to the current source. When the switch H85 is in this position, i. e. the arm contacting with contact ltd, the coils lid, H9, 62d and ill will not receive current fro the source 53% and hence current will be induced in the vessel I d2 only by means of the coils M3 to ill.

Fig. 16 of the drawings illustrates the heating effect obtained when the arms of switches i535 and M8 are both in the down-position. In this position of the switches current will be supplied from the current source use through line I32 to coil Sill, through coils M3, M5, H5, H6 and ill-in series, and line I183 to the arm ltd of switch I35,

-thence to contact- 638 of the switch i235, and

In Fig. 14 there is showna wiring diagram adapted for the apparatus illustrated in Figs. 10-42. In'this diagram I30 represents a suitable alternating current supply. A main switch I M is provided to control the supply of current" from supply I30. This switch may be provided with an overload throw-out. if desired. The current source I30 is connected by 'jmeans of source are by means of line I31.

through line G88 to coil lid, passing through coils lid and lid in series, and from coil M9 through linelldl to contact M2 of switch S8, throughswitch i 38 and back to the current With this arrangement of the coils, currentswill be induced in the vessel inthe same portions thereof as in Fig. 15. But the inductance at the portion 01 the vessel adjacent coils i it to l I9 will be higher than formerlmfcompared with that in the lower portions or the vessel, because of the added induction cells .6 l8 and 5 I9, and consequently this portion oi the vwsel will receive a greater pro portion of the heat. 1

With the switches i the position indicated. in Fig.17, the current supplied from source 130 through line I132 travels through coils IE3 to H1 in series, through line E33, and switch arm I36, thence through, contact I38 line I39, coils H8 and M8 in series, and through line I40 to coil I20, from coil I20 through line I to contact I of the switch 543, thence it returns through switch ern: IdBnndline ill to the current source I30. In this arrangement of the circuit only the coils II: to I20 are connected in the circuit, and ourrents are induced in thevessel only by these coils;

consequently the maximum heating is applied to the portions of the vessel adjacent to these coils. With the arm to! switch I35 in the down position and the arm of switch I43 in the up position previous arrangements. 7 It then passes from coil I" through line "I, through arm I of switch I, thence to contact Ill, through line I" to coil Ill and inseries through coils H8 and I, line .the most intense heat may be applied, in the second modification, to that portion of the vessel which requires it. If the vessel is filled with nq' uid, for example, heat may be applied by means of all of the induction coils as indicated in Fig. 18. with the apparatus designed as illustrated, this "arrangement results in the greatest application of heat at the bottom of the vessel, the intensity gradually diminishing up the vessel, but this may be altered by varying the construction or design of the coils or vessel. If on the other hand the liquid level is reduced or if for another reason it is desired to reduce the extent of application of heat, the coil M or coils 2| and 22 or the coils l8 to 2| may be cut out of the circuit by suitable operation of the switches.

From the foregoing description of the form of the invention illustrated in the drawings it will be apparent that the location and area of the vessel in which heat is developed and the amount of heat produced may be selectively varied by operation oi the switching mechanism controlling the flow of current through the conductor which constitutes the primary for the heater and the various sections thereof.

While I have illustrated and described a preferred form ofmy invention by way of illustration, it will be apparent that the invention may be used for heating metallic articles other than vessels or stills. It will also be apparent that the invention is not limited to the use of the specific circuit arrangements illustrated and described but is capable ofa wide range of variations without departing from the spirit and scope thereof.

I claim:

1. An electrical heating apparatus comprising a member to be heated, a conductor encircling said member, in inductive relation therewith, a source of alternating current, a plurality of elements connecting said conductor to said source of alternating current, selective means for varying the amount and location of heat generated in said member including a switch movable to vary. the flow of current through said conductor.

2. An electrical heating apparatus comprising a member to be heated, a conductor encircling said member, in inductive relation therewith a source of alternating current, a plurality of elements connecting said conductor to said source of alternating current dividing said conductor into a plurality of sections, and means for varying the area of said member in which induced currents are generated including a switch in circuit with saidconductor movable to control the flow of current throughone of the sections of said conductor.

' 3. An electrical heating apparatus comprising a member to be heated, a conductor encircling said member in inductive relation therewith, a source of alternating current, a plurality of elements connecting said conductor to said source of alternating current dividing said conductor into a plurality of sections, and a circuit control deviceselectively movable to connect sections of said conductor to said source of current in series and in parallel and to disconnect one or more of -said sections from said source of current. A

4, electrical heating device comprising a member to be heated, an electrical conductor in inductive relation with said member, a source of alternating current, elements connecting said conductor to said source of current, a second conductor in inductive relation with said member, ele- -ments connecting said second conductor tosaid source oi! current at a lurality of points dividing said second conductor nto a plurality of sections,

means for selectively connecting either or both of said conductors to said source of current, and a switch movable to vary the current flow. in the sections of the second conductor independently, of the current flow in said first mentioned conductor.

5. An electrically heated still comprising a metallic vessel, an electrical conductor encircling said vessel in inductive relation therewith, a source of alternating current, elements connecting said conductor to said source of current, and selective means for varying the amount and location of heat generated in said vessel, including a member movableto control the flow of current throu h said conductor.

6. .An electrically heated still comprising a metallic vessel, an electrical conductor encircling the upper portion of said vessel in conductive relation therewith, an electrical conductor encircling the lower portion of said vessel in conductive re- 2 latlon therewith, a source of alternating current, electrically conductive elements connecting said conductors to said source of current, means for varying the amount and location of heat generated in said vessel including a member movable to vary the currentflow in one of said conductors independently of the other.

7. An electrical heating apparatus comprising a member to be heated, a conductor encircling said member in a plurality of turns, means carried by said member supporting said conductor, insulating elements carried by said means spacing the turns of said conductor from each other, a source of alternating current, and means connecting said conductor to said source of current.

8. An electrical heating apparatus comprising a member to be heated, a conductor encircling said member in a plurality of turns, a plurality of rods extending transversely of said conductor adjacent thereto, means spacing the turns oi said conductor from each other, means securing said conductor in position with reference to said rods, 7

a source of alternating current, and means connecting said conductor to said source of'alternating current.

9. An electrical heating apparatus comprising a member to be heated, a conductor encircling said member in a plurality of turns, a plurality of rods extending transversely of said conductor adjacent thereto, means spacing the turns of said conductor from each other, means seeming said conductor in position with reference to said rods, a source of alternating current, means connecting said conductor to said source of current at a plurality of points dividing said conductor into a plurality of sections, and a switch movable to vary the current iiow in one of said sections inspacing the turns of said conductor from each other and securing said conductor in position with reference to said rods, a source of alternating current, and means connecting said conductor to said source of alternating current.

11. An electrically heated still comprising a.

metallic vessel adapted to receive liquid to be distilled,- a flange .formed integral with said vessel and extending outwardly-therefrom, vertically extending rods supported by said flange and positioned about said vessel, an electrical conductor encircling said vessel in inductive relation therewith, insulating means carried by said rods engaging said conductor to hold the same in position, a source of alternating current, elements connecting said conductor to said source of current and selective means for varying the of the induced current of maximum magnitude toconform to a desired change in location of heating efi'ect of maximum intensity.

13. A method of distilling liquids which comprising introducing the liquid to be distilled into a metallic vessel, inducing current flow in said vessel by the action of alternating current, removing vapors of said liquid from said vessel, and

diminishing the area of the vessel heated as the level of the liquid in said vessel is lowered by the distillation of liquid therefrom.

14. A method of distilling liquids involving variation in the liquid level during the distillation, which comprises introducing liquid to be distilled into a metallic vessel, inducing electrical currents in said vessel whereby said vessel and liquid are heated, controlling the location ,tnd amount of current induced in said vessel during distillation of said liquid, and maintaining the aoeaeae 7 portion of said vessel in contact with said liquid at a temperature substantially higher than the temperature of that portion of the vessel which is in contact with the vapors produced in distilling said liquid.

15. A method of distilling liquids which com-' prises introducing a liquid to be distilled into a metallic vessel, inducing current flow in the walls of said vessel by the action of alternating current, removing vapors of the liquid being distilled from said vessel, decreasing the current induced in the upper portion of the walls of said vessel as the level of the liquid in saidvessel is lowered, and maintaining the current induced in the portion of the vessel in contact with said liquid substantially constant.

16. A methodot. heating a liquid in a metallic vessel in whichtheportion of the vessel occupied by liquid varies during the heating, which method comprises inducing current flow in said vessel by the action of alternating current and controlling the flow of current in such a manner that the zone of most intense heating is restricted to the portion of the vessel occupied byliquid.

1'7. A heating apparatuscomprising a vessel adapted to contain material to be heated, an induction coil encircling-a lower portion of said vessel, a second induction coil encircling an upper portion of saidvessel, each of said coils being adapted to induce an electrical current in a substantial portion of said vessel, means for supplying alternating current to said induction coils, and means for independently 18. An electrically heated apparatus comprising a metallic vessel, supporting legs circumferentiaily disposed thereabout, coil supporting members mounted on said legs, a series of induction coils-disposed about said vessel adjacent to difi'er'-,

ent portions thereof and supported by said supporting legs, means for'connecting a plurality of the coils in series in an electric circuit, and means for removing one of said coils from the circuit while retaining another coil in the circuit.

GEORGE J controlling the current supplied to each of said coils. 

